The present invention relates to a semiconductor integrated circuit device, more particularly to a semiconductor integrated circuit device provided with a read-only memory for storing information concerning defective bits for the replacement of defective bits in a semiconductor memory device, etc., with redundant bits.
In general, in a semiconductor memory device, an operational test is conducted at the wafer stage to detect defective bits. The defective bits are switched with separately provided redundant bits, thus preventing reduced yield of the devices. Such a semiconductor memory device stores the information concerning the defective bits and, when these defective bits are accessed, operates so that the redundant bits are accessed. Therefore, when defective bits are detected at the wafer stage, the information concerning the defective bits must be stored in the read-only memory (ROM) using fuses, etc. For a ROM to be used for this purpose, it is necessary that the writing be performed reliably, the space occupied on the semiconductor chip be small, and the operation after the writing be performed reliably.
In a conventional semiconductor integrated circuit device, a fuse-blown type ROM is used to store the information concerning the defective bits, and the write operation to the ROM is effected by melting one or more fuses by supplying a large current to the fuses via one or more switching transistors.
This device has a drawback in that the fuses of the ROM cannot be reliably melted because the current flowing therethrough is limited by the current capacity and the withstand voltage of the switching transistors.
There is known another semiconductor integrated circuit device using a fuse-blown type ROM, wherein the write operation to the ROM is effected by supplying a large current to each fuse of the ROM directly via a probing pad.
This device has disadvantages in that the degree of integration is deteriorated because it is necessary to provide a probing pad for each fuse.